As it is well known, there is global concern for the release of contaminants to the atmosphere, a trend that has materialized in the imposition of stricter standards on motor vehicle exhaust gas emissions. Particularly the European Union has adopted restrictive regulations for application within 2005 to both the exhaust emissions and the fuel consumption of motor vehicles. The most significant of these regulations—some of which are already in force while others are due to come in force soon—are summarized here below:
Euro I (91/441): for reduced emissions of pollutants, this directive has made the installation of a catalyzed exhaust system compulsory for all vehicles, registered since Jan. 1, 1993.
Euro II (96/69): applies to models registered since 1996 and sold up to December 2000.
Euro III (98/69): vehicles registered since Jan. 1, 2001 comply with this directive. Besides the problem of polluting emissions, since less pressing, an OBD (On-Board Diagnostics) system is made compulsory to detect malfunctions. Completion of any repairs within a given distance travelled, in number of kilometers, is strictly enforced. This directive, that applies to gasoline powered vehicles, is to become in force for diesel engines in 2003.
Euro IV (98/68B): scheduled for Jan. 1, 2005.
Euro V (2001/27/ EC): scheduled for Jan. 1, 2008.
An estimate of overall emissions is given in Table 1 below; combined technical data (emission factors) and active data (total number of kilometers travelled by the vehicle) have been supplied by the user of a passenger car, and enter the computation:
TierYearCOHCHC + NoxNOxPMDieselEuro 119922.72—0.97—0.14Euro 2-ID119961.0—0.7—0.08Euro 2-DI19991.0—0.9—0.10Euro 32000.010.64—0.560.500.05Euro 42005.010.50—0.300.250.025Petrol(Gasoline)Euro 32000.012.300.20—0.15—Euro 42005.011.00.10—0.08—
Total emission is the sum of the emissions from three different sources, where a first source is the engine in its steady thermal range (warm), a second source is the engine in its warm-up range (cold), and a third source is evaporated fuel. Distinguishing the first two sources is of fundamental importance because considerable emission variations can be observed between the two. During warm-up, the emission of pollutants often exceeds that of the same engine once warmed up, and the pollutant assessing criteria differ. Total emission is calculated by the following formula:ETOTAL=EHOT+ECOLD+EEVAPwhere, ETOTAL is total emitted pollutants of any kind for space and time resolution of the application; EHOT is emission in the steady range of engine operation (warmed up); and ECOLD is emission in the warm-up transitory range of engine operation (cold start). EEVAP is emission of the fuel evaporation.
Vehicle emissions are heavily dependent on the engine RPM; e.g. when driving in the city, over country roads, or highways. The pollutants released by an internal combustion (IC) engine are the outcome of incomplete combustion of the air/fuel mixture; or result from compounds, such as lube oil and lube oil additives, reacting together in the combustion chamber; or originate from inorganic components, such as sulphur present in diesel fuel. A major problem with gasoline engines is the emission of nitrogen and carbon compounds, such as NOx and CO2. With diesel engines, additional to NOx compounds, carbon is released as DPM (Diesel Particulate Matter). DPM is negligible in gasoline-burning engines.
DPM is a complex mixture of liquid and solid matter, and has for its main constituent solid carbon that is generated from incomplete combustion within the cylinder. DPM usually comes in three fractions: dry carbon/sooty particles, SOFs (Soluble Organic Fractions), and acidic sulphur particles. FIG. 1 schematically shows a clump of particulates, with the nuclei of the materials contained therein clearly in view.
DPM composition is tied to the engine type and the engine operating conditions, foremost among which are speed and loading. Table 2 below shows DPM size and corresponding classification:
RATINGDIAMETER D (mX10−6)PM 10<10Fine<2.5Ultra-fine<1.0Nano-size particles<0.05
Mainly responsible for the formation of NOx compounds in both diesel and gasoline engines is the combustion chamber reaching a sufficiently high temperature to cause the nitrogen that is present in the combustion air to break down and re-combine with oxygen to yield nitrogen monoxide (NO) and dioxide (NO2). On the other hand, any attempt at keeping the temperature low inside the combustion chamber to attenuate the formation of NOx is bound to result in increased DPM release. A major problem with diesel engines is the trade-off between released NOx and DPM. Reducing this effect is the main objective of diesel emission control, restrictions on DPM emission being even more stringent.
The state of the art offers some approaches to the problem of reducing the polluting emissions from endothermic engines. Such prior proposals apply in different ways to diesel and gasoline engines and include improvements of mechanical as well as electronic quality. A first example of one of these approaches reduces exhaust gas pollution by adopting an electronically controlled exhaust gas re-circulating system (EGR). An electronic control system generates a signal to open a valve placed in an exhaust gas re-circulation duct so as to direct the exhaust gases back into the engine cylinders, thereby lowering the content of NOx compounds.
In the instance of gasoline engines, also known is to use a lambda probe that cooperates with tervalent catalysts. The latter are capable of converting polluting gases to less harmful gases by an oxidation-reduction process. A catalytic converter usually comprises a metal enclosure containing an essentially honeycombed ceramic or metal substrate coated with a film of γ-alumina, also known as the “wash coat”, 40 to 50 μm thick. This support is deposited on, using appropriate techniques, an active catalytic material consisting of a mixture of noble metals such as platinum, palladium, or rhodium. These metals are deposited in small amounts but spread over the support at a high rate of specific coverage. FIG. 2 schematically shows the resultant ply structure to an enlarged scale.
A lambda probe is fitted in the re-circulation duct between the catalyzer and the engine to instantly read the proportion of residual oxygen in the gas flow that is sweeping past its electrodes. An electric signal is thus generated and supplied to an engine control unit that will process it to adjust the air/gasoline ratio for optimum catalytic conversion. FIG. 3 schematically shows this control arrangement for gasoline engines. More recently, a variable geometry turbo (VGT) has been added to the electronic EGR control, wherein the rotor blade angle is varied and so is the flow of exhaust gas through it according to engine RPM.
For diesel engines to meet Standard EURO III (2000), a high-pressure fuel injection system has been developed, known as the CR (Common Rail) system, wherein a pressure of approximately 1350-bar is attained to effectively lower both pollutant emissions and fuel consumption. This CR system generates injection pressures of a sufficiently high order to atomize the fuel in the combustion chamber such to obtain an almost perfect fuel/air mixing, resulting in reduced unburned exhaust gases and particulates.
A CR system basically comprises a high-pressure radial-piston fuel pump, an accumulator (rail), a series of injectors connected in a high pressure conduit, a control unit, actuators, and a plurality of sensors. The pump maintains the fuel at a high pressure to force it into the accumulator or “rail”, the latter serving all the injectors by functioning as a high-pressure reservoir. Some of the fuel is then injected into a respective combustion chamber through electro-magnetically operated injectors, and some is returned to the tank for re-circulation.
The circulating flow is determined and balanced by an electronic unit comparing the pressure detected by the sensors with predetermined reference values, and adjusting for any overpressure by diverting the excess fuel back to the tank. The indications from the sensors enable the unit to meter the amount of fuel that is injected so as to suit the engine load and RPM, thereby affording a highly flexible form of fuel control. The pressure level is adequate to meet the engine requirements at all RPM, unlike traditional systems where the pump was driven off the engine, and the pressure depended on the engine RPM and was almost never an optimum level, especially at low RPM.
Current CR-equipped engines have only two injections per cycle (a pilot injection and a main injection). However, recent developments have made the injection system more flexible, in the sense that a better blended mixture has been achieved by splitting the main injection into multiple injections and changing the geometry of the intake conduits for swirl effect.
It will only be possible to conform with impending EURO IV (2005) directives when both the mechanical and electronic aspects of current control systems are further improved. In this respect, conversion for multiple injection and rail pressures of up to 1600 bar is regarded an essential measure.
In turn, injectors should be redesigned for improved mechanics and smaller injection ports. Also contemplated is the installation in the combustion chamber of a precision type of pressure sensor for high temperatures, which would feed back pressure signals for implementing engine control algorithms of far greater accuracy. It is held by many that catalytic post-treatment of exhaust gases will be unavoidable on both gasoline or diesel engines. Each engine has requirements of its own as to reduced emissions, which means that its catalyzer must be suitably tailored, varying several parameters: chemical functions, type of impregnant, amount and type of noble metal, substrate porosity, location in the exhaust line, etc. In either engine types, measuring the exhaust emissions would entail the provision of exhaust sensors that, additional to being themselves fairly expensive items, involve further service and maintenance costs.
To keep the added cost represented by such sensors low, one might think of providing a virtual sensor based on an accurate model of the internal combustion engine operation, be it a diesel or a gasoline type. However, sensors of this kind require modelling to a high degree of accuracy if all the quantities involved in an engine operation and their varying through each engine cycle are to be taken into account. Briefly, using a virtual sensor is bound to reflect on very high processing costs due to the highly complex nature of the model.
The underlying technical problem of this invention is to provide a virtual sensor of the exhaust emissions from a fuel-injection endothermic engine with structural and functional features appropriate to overcome the limitations of the prior art. In particular, this sensor should be simple, effective, and convenient for retrofitting to an existing electronic injection control unit already in use in the motor-vehicle.